How would it be possible to track back to the origin source if the transactions were mixed, broken down and distributed across random intervals- all to different addresses?
Magic. IT would be very difficult to tell and maybe even impossible in some cases but it all depends on how well they're mixed.
It would be impossible in all cases unless the mixer sites store information on the customers as they don't forward payments but mix with other payments and the original will have no connection with the final one.